Motor of rotor with built-in permanent magnet

ABSTRACT

The present invention is a motor of rotor with built-in permanent magnet, which includes an annular stator and a rotor. The annular stator has a cylindrical interior into which the rotor is inserted. A space is formed between a circumference surface of cylindrical interior and rotor. The rotor further includes a rotor core, and a plurality of openings are formed surrounding the rotor core. Each opening is with two parallel surfaces, a top surface and a bottom surface, and each of them is a flat plate figure. A suitable distance is between two side surfaces and an outer circumference of the rotor, and the two side surfaces of adjacent openings are spaced by a channel fo suitable width. A plurality of permanent magnets are arranged in openings by way of interlaced magnetic poles, and the shape of permanent matches the shape of the opening.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 10/036,504,filed on Jan. 7, 2002, entitled “A Motor of Rotor With Built-InPermanent Magnet” and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is a motor of rotor with built-in permanentmagnet, especially refer to a rotor which has no flux-barrier holes, andcan effectively prevent phenomena of short-circuiting of magnetic flux.

2. Background of the Invention

As science is advanced day by day, the needs of normal life tend toshort, light, thin and small products; the improvement of generalmechanical mechanism is toward to high efficiency. The design oftraditional motor torque of surface mount motor (T=Pn×φa×Ia, where Pn ispole number, φa is magnetic flux on d-axis, Ia is electric current ond-axis) is not suitable to electrical vehicles and compressors ofrefrigeration and air condition fields. Thus, adding an permanent magneton rotor to promote total torque of traditional motor device, thus thetotal torque (T=Pn[φa×Ia+0.5(Ld−Lq)×Id×Iq], where φa×Ia is magnetictorque producing from permanent magnet of rotor, 0.5(Ld−Lq)×Id×Iq isreluctance torque producing form inductance difference of axes d and q)is with both magnetic torque and reluctance torque. Thus, under samevolume condition, the motor of rotor with built-in permanent magnetwhich output torque and running efficiency are better than thetraditional surface mount motor with magnetic torque. In another words,under same output torque condition, the volume of motor of rotor withbuilt-in permanent magnet is smaller than the volume of the traditionalmotor with magnetic torque.

Please refer to FIG. 1A, which is sectional structure view of a 4-polemotor of rectangular piece permanent magnet in prior art. Wherein, themotor of rotor with rectangular piece permanent magnet comprises of: aannular stator 1 and a rotor 2. A cylindrical capacity with suitablediameter is set in the annular stator 1, and its circumference surfaceis with teeth 11 and openings 12. Each tooth 11 and each slot 12 areinterlaced each other. There are some wires winding around slot 12. Therotor 2 is a cylindrical structure set in the cylindrical capacity, andthere is an air gap 13 between rotor 2 and the circumference surface ofcylindrical capacity. Rotor 2 further includes a cylindrical rotor core20, and four rectangular openings 21 which are set surrounding the rotorcore 20. Four relative rectangular solid permanent magnets 22 justinsert and match into four rectangular openings 21. The arrangement forfour rectangular solid permanent magnets 22 and four rectangularopenings 21 is interlaced. When annular stator 2 is electrified, slot 12produces magnetic forces in order for rotating annular stator 2. Fourrectangular piece permanent magnets 22 are easily made and thusmanufacturing cost is lower, but the arrangement causes serious magneticflux leakage and cogging phenomena. Flux leakage lowers down effectivetorque and motor efficiency. Cogging phenomena increases motor coggingtorque, and vibration and noise are both increased as well. Therefore,several flux-barrier holes 211 are drilled on two ends of eachrectangular piece 21 in prior art, but the cost is higher, and solvingthe aforesaid shortcomings is not much (showing as FIGS. 1B and 1C).Besides, because of the flux-barrier holes 211, permanent magnet 22 ishardly fixed when permanent magnet 22 inserting into rectangularopenings 21, and thus viscose is a need. Obviously, motor assemblybecomes very complicated.

Please refer to FIG. 2, which is sectional structure view of motor ofarc piece permanent magnet in prior art. Wherein, four arc piece pieces23 are set surrounding rotor core 20, and four relative arc piecepermanent magnets 24 are inserted and matched into the four arc piecepieces 23. The arrangement for four arc piece permanent magnets 24 andfour arc piece pieces 23 is interlaced. Generally, for producing greaterreluctance torque, the arrangement in rotor core 20 is that top arc ofarc piece 23 is toward to rotor center of motor. Two ends of each arcpiece 23 are toward to contour of rotor core 20. The figures of the twoends of each arc piece 23 are based on arc curvature of rotor core 20.Although the design highly decreases magnetic flux leakage and promotesoutput torque, the arc curvature of arc piece permanent magnet 24 iscomplicate, and it is not easily formed in manufacturing. The cost ofarc piece permanent magnet 24 for easily inserting and matching into arcpiece 23 with no loose is much higher than the cost of rectangular piecepermanent magnet, further, cogging torque is also bigger to simplyproduce vibration.

As a conclusion of aforesaid prior arts, the shortcomings for themcannot be solved one by one, thus the present invention will bedescribed as below to figure out the defects in prior art.

BRIEF DESCRIPTION OF THE INVENTION

The first object of the present invention is to offer a motor of rotorwith built-in permanent magnet, and the motor is with low cogging torqueto be sure of that the functions of promoting running efficiency andlowering vibration noise are working properly.

The second object of the present invention is to offer a motor of rotorwith built-in permanent magnet, the motor is easily and flexiblydesigned and formed, thus the cost is certainly down.

To reach the aforesaid objects, the present invention comprises of: arotor core and a plurality of permanent magnets.

The above said rotor core is a cylindrical structure, which issurrounded by a plurality of openings. Each opening is with two parallelsurfaces, a top surface and a bottom surface, and each of them is a flatplate figure. The top surface is adjacent to contour of rotor core andextends along the circumference contour forming a side surface. There isa suitable distance between the side surface and the contour of rotorcore. Two adjacent side surfaces are with a certain width of a channel.

The shape of the above permanent magnet is able to meet with theopening, and both of them can be matched each other.

Another preferred embodiment of the present invention is a rotor withbuilt-in permanent magnet, the motor comprises of an annular stator anda rotor.

The above said annular stator is set a cylindrical capacity with asuitable diameter, and the circumference surface of the cylindricalcapacity is set a plurality of teeth and a plurality of openings.

The rotor is a cylindrical structure, and it is set in the cylindricalcapacity. There is an air gap between rotor and circumference surface ofcylindrical capacity. Rotor further includes a rotor core, which is acylindrical structure, and there are a plurality of openings installedaround rotor. Each opening is with two parallel surfaces, a top surfaceand a bottom surface. The top surface is adjacent to contour of rotorcore and extends along the circumference contour forming a side surface.There is a suitable distance between the side surface and the contour ofrotor core. Two adjacent side surfaces are with a certain width of achannel and a plurality of permanent magnets. The shape of the abovepermanent magnet is able to meet with the opening, and both of them canbe matched each other.

Other features and advantages of the invention will be apparent from thefollowing description of the preferred embodiments thereof, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is sectional structure view of motor of rectangular piecepermanent magnet in prior art.

FIG. 1B is output torque diagram of motor of rectangular piece permanentmagnet in prior art.

FIG. 1C is cogging torque diagram of motor of rectangular piecepermanent magnet in prior art.

FIG. 2 is sectional structure view of motor of arc piece permanentmagnet in prior art.

FIG. 3A is 3-D structure view of the first preferred embodiment of rotorwith built-in permanent magnet for the present invention.

FIG. 3B is 3-D structure view of the second preferred embodiment ofrotor with built-in permanent magnet for the present invention.

FIG. 4A is sectional structure view of the first preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 4B is partial enlarged view of the first preferred embodiment A ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 4C is output torque diagram of the first preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 4D is cogging torque diagram of the first preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 5A is sectional structure view of the second preferred embodimentof motor of rotor with built-in permanent magnet for the presentinvention.

FIG. 5B is partial enlarged view of the second preferred embodiment B ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 5C is output torque diagram of the second preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 6A is sectional structure view of the third preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 6B is cogging torque diagram of the third preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 7 is sectional structure view of the fourth preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 8 is sectional structure view of the fifth preferred embodiment ofmotor of rotor with built-in permanent magnet for the present invention.

FIG. 9A is the sixth preferred embodiment of motor of rotor withbuilt-in permanent magnet for the present invention.

FIG. 9B is the sixth preferred embodiment of motor of rotor withbuilt-in permanent magnet for the present invention.

FIG. 10 is a cross-sectional enlarged view of the second preferredembodiment of motor of rotor with built-in permanent magnet for thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The main features of motor of rotor with built-in permanent magnet are:a plurality of nearly rectangular-shaped openings are formed surroundinga outer-skirt of a rotor core; each opening is formed with the sameshape as the rectangular permanent magnet; each opening is with twoparallel surfaces, namely a top surface and a bottom surface, and eachof them is a flat plate figure; the top surface is adjacent to a outercontour of rotor core and extends along the contour so as to form a sidesurface substantially parallel to and nearby the outer contour of therotor core; two adjacent side surfaces are spaced-apart with a certainwidth of a channel. Based on the design, manufacturing cost and motorcogging torque can be lowered down; on the other hand, output torque isincreased.

Please refer to FIGS. 3A and 3B, which are 3-D structure views of thetwo preferred embodiments of rotor with built-in permanent magnet of thepresent invention. Wherein, the rotor 2 with built-in permanent magnetcomprises of: a rotor core 20 and a plurality of permanent magnets 29.The rotor core 20 is a cylindrical structure. As showing in FIG. 3A, thecylindrical structure could be as an integrally formed solid siliconsteel, of course it could be made by other good permeability materials.As showing in FIG. 3B, the preferred cylindrical structure could beformed via accumulation of a plurality of silicon steel sheet pieces 28.The silicon steel sheet piece 28 is made of silicon steel via stamping.Each silicon steel sheet piece 28 has a plurality dents 281, each denthas a convex point on a first surface of the silicon steel sheet piece28, and a concave point on a second surface. The accumulation of aplurality of silicon steel sheet pieces 28 forms the rotor core 20. Thesteel sheet pieces 28 can be made by a stamping process to make andmatch the plurality of dents 281 so as to fix and form the cylindricalstructure. A center of rotor core 20 is further designed a central axialhole 26, and a plurality of arc troughs 27 are distributed surroundingthe central axial hole 26. Arc troughs 27 can decrease weight andmaterial cost.

A plurality of openings 25 are set surrounding an outer-skirt of therotor core 20, and the openings 25 can be inserted and matched withpermanent magnets 29. The shape of permanent magnet 29 fits with theopening 25, and permanent magnet 29 takes the way of interlaced magneticpoles to be contained in opening 25. In the preferred embodiments of thepresent invention, the numbers of permanent magnets 29 and openings 25are four for each of them; on the other hand, the containing arrangementof interlaced magnetic poles makes the numbers be more than two, forinstance, four, six, eight, etc.

Please refer to FIGS. 4A and 4B, which are sectional structure andpartial enlarged views of the preferred embodiments of motor of rotorwith built-in permanent magnet. Wherein, the motor of rotor withbuilt-in permanent magnet comprises of: an annular stator 1 and a rotor2. The annular stator 1 is with a cylindrical capacity of a suitablediameter. The circumference surface of the cylindrical capacity is withteeth 11 and slots 12. Each tooth 11 and each slot 12 are interlacedeach other. Slot 12 could be designed based on different needs, andbecause it is winded around with multi-phase coils. Differentarrangements of permanent magnet 29 and opening 25 of different rotor 2are mostly same and similar to the aforesaid rotor with permanentmagnet. Therefore, persons knowing the technology well easily change thevariable embodiments, and no further discussion is for the part.Following description focuses on different designs, thus same or similarelements are given same names and numbers.

The rotor 2 is a cylindrical structure, which is set in a cylindricalcapacity, and there is a space 13 between the annular stator 1 and therotor 2. When annular stator 1 is electrified, slot 12 produces magneticforces in order for rotating rotor 2 in cylindrical capacity. In thepreferred embodiment, rotor 2 includes the rotor core 20 and a pluralityof permanent magnets 29. Rotor core 20 is a cylindrical structure, andthe plurality of openings 25 are set surrounding a cylindricalstructure, and the plurality of openings 25 are set surrounding aouter-skirt of the rotor core 20. The shape of permanent magnet 29 fitswith opening 25, and the arrangement of the way of interlaced magneticpoles for permanent magnets 29 are contained in openings 25.

In the preferred embodiment, opening 25 is designed similar to arectangular or trapezoid to fit with permanent magnet 29 of the samerectangular or trapezoid for easily inserting permanent magnet 29 intoopening 25. The opening 25 is with two parallel surfaces, a top surface251 and a bottom surface 252. The top surface 251 is formed on a side ofthe opening closest to an outer circumference of the rotor core andextends a length of the rotor core. The opening has a side surface 253which is substantially parallel to the outer circumference of the rotorcore 20. In this preferred embodiment, the side surface 253 is an arcsurface, which curvature is equal to a circumference contour of therotor core 20. Of course, a polygon arc surface approaching thecurvature of the circumference contour could reach same function. Asuitable space 255 is between side surface 253 and the outercircumference of the rotor core 20. The space 255 is small and plays therole of flux-barrier, but easily made, and it performs well when thedistance smaller than 0.7 mm. Two adjacent side surfaces 253 are spacedby a channel 254 with suitable width. The width of the channel 254 issmall and functions as a flux-barrier. In the preferred embodiment,channel 254 performs well when the width is smaller than 0.7 mm.

In the aforesaid preferred embodiment, two ends of side surface 253separately connect to top surface 251 and bottom surface 252. Forpreventing permanent magnet 29 damaged in manufacturing, the adjacentparts of side surface 253 are trimmed to be arc-shaped; of course, across section of permanent magnet 29 matches a cross section of theopening so that the permanent magnets can be inserted into the opening.

Please refer to FIGS. 4C and 4D, which are the output torque and coggingtorque diagrams of motor of rotor with built-in permanent magnet of thepresent invention. Wherein, the output torque and cogging torque of thepreferred embodiment of motor of rotor with built-in permanent magnetcompares with the prior art's in the figures. Under the conditions ofthat the annular stator 1 and the rotor 2 in prior art which dimensionof outer diameter is same as the preferred embodiment's of the presentinvention, and two thicknesses of permanent magnets of the prior art andthe preferred embodiment for the present invention are same, thus theshowing as in figures, the comparison of the embodiment and the priorart of FIG. 1B is that the maximum output torque of FIG. 1B is 25 NT-mand the maximum output torque of the present invention in FIG. 4C is 30NT-m, thus the promotion rate is over 15%; the maximum cogging torque ofFIG. 1C is 0.7 NT-m and the maximum cogging torque of FIG. 4D is 0.5NT-m, thus the decreasing rate is over 25%.

Please refer to FIG. 5A to 5C, which are another preferred embodiment ofmotor of rotor with built-in permanent magnet of the present invention.Wherein, the thickness of the permanent magnet 29 is changed, and anparallel channel side surface 256 is in between the side surface 253 andthe bottom surface 252, thus side surface 253 and the parallel channelside surface 256 are taper arc surfaces, and a channel 254 between twoadjacent permanent magnets 29 is strip shape. For preventing permanentmagnet 29 damaged in manufacturing, the side surfaces 253 of opening 25are arch-shaped; of course, the relative locations on permanent magnet29 are arc-shaped as well. Wherein, the dimensions of outer diameters ofannular stator 1 and the rotor 2 of the preferred embodiment is the sameconditions as the preferred embodiment's for FIG. 4A to 4D, and themaximum output torque of the preferred embodiment is promoted to 31NT-m, thus the promotion rate is about 5%.

Please refer to FIGS. 6A and 6B, which are the third preferredembodiments of motor of rotor with built-in permanent magnet of thepresent invention. Wherein, a parallel channel side surface 256 a is setbetween side surface 253 a and bottom surface 252 a. Parallel channelside surface 256 a is modified to become a single arc surface or amultiple arc surface. The dimensions of outer diameters of annularstator 1 and rotor 2 are same as the embodiment's dimensions in FIG. 4Ato 4D. The maximum cogging torque is lowered down to 0.46 NT-m, and thecomparison to the embodiment in FIG. 4A to 4D is about 8% down. Theabove values are under the conditions of that both of the rotor lengthper meter and magnetic flux are identical, and then having them. Ofcourse, changing some of the values is to adjust a little of result.Therefore, persons knowing the technology well easily change thevariable embodiments, and no further discussion is for the part.

Please refer to FIG. 7 to FIG. 9B, which are the fourth preferredembodiment of motor of rotor with built-in permanent magnet. Theembodiment in FIG. 7 is that permanent magnet 29 is closer to contour ofrotor core 20 and the thickness of permanent magnet 29 is greater,therefore, the side surface 253 b is greater than the side surface 253in FIG. 5A, and the channel 254 b between two adjacent permanent magnets29 is short strip structure. The embodiment in FIG. 8 is that permanentmagnet 29 is closer to contour of rotor core 20, thus the parallelchannel side surface 256 c is smaller, and the section of channel 254 cbetween outer contour of rotor core 20 and circle center is narrower. Asshowing in FIG. 9A, which is the amended one of FIG. 4 b, another words,the side surface 253 in FIG. 4 b is amended to the side surface 253 dwith straight line in FIG. 9A; same theory, the side surface 253 in FIG.5 b is amended to the side surface 253 e with straight line in FIG. 9B.Therefore, persons knowing the technology well easily change thevariable embodiments, and no further discussion is for the part.

As shown in the FIG. 10, when the outer radius of the motor rotor Ro isdetermined, in order to meet the requirement of magnetic flux reduction,and due to the constrain of assembling, the minimum ΔR will be obtained.According to the practical experience in manufacturing, ΔR≦0.7 mm willprovide the optimal solution. Therefore the radius Rm of the maximum arc(shown as AB and A′B′) of the magnet can be obtained, which meansΔR=(Ro−Rm)≦0.7 mm.

Next, the thickness t has to be determined, according to the drawing,t=t1+t2, wherein t1 and t2 can be 0, so, the length of AA′ (L1) is equalto 2(Rm*sin θ1), which means L1=2*(Rm*sin θ1) and L3=2*((Rm*sinθ2)−(t2*tan θ2)), wherein t1=Rm*(cos θ1−cos θ2) and L3=CC′.

From above, when t1=0, θ1=θ2, and L1=L2(BB′), the shape of magnet isshown as in FIG. 8. And when t2=0, L3=L2(BB′), the shape of magnet isshown as in FIGS. 4 a and 7. When t1≠0, t2≠0, the shape of magnet isshown as in FIG. 5 a.

From the drawing (FIG. 10), as seen, d=Rm*cos θ2, θ2 is determineddepending on the number of magnet gate of the motor and the requirementof the performance, when the number of magnet P≧4, θ2=(360/P)−Δθ,wherein Δθ is the angle between the gap of two adjacent magnet towardthe axis of the rotor, which means the gap is around Rm*Δθ, in theexperimental testing, the gap ≦0.7 mm will produce the best performance,which also means Δθ≦((0.7/Rm)*(360/π)). And when P<4, θ2 will not belimited, the value will be determined by the performance desired and theouter radius of the rotor of the motor.

As the aforesaid mention, the motor of rotor with built-in permanentmagnet of the present invention is with the functions of flexible designand easy formation. The motor runs with low cogging torque and highoutput torque for promoting efficiency and decreasing vibration noise,and the cost is also low. Thus, the present invention totally figuresout the shortcomings of prior art.

The above descriptions are the preferable embodiments of the presentinvention. The covered scopes of the present invention are notrestricted on the embodiments shown in the present invention. All thechanges according to the contents of the present invention, such as: thechange of shapes or locations of the arrangement of the fasteningstructures, etc., the generated functions and characteristics similar tothose of the embodiments of the present invention and any ideas thoughtby the persons well-known such technologies are all within the scopes ofthe present invention.

1. A motor having a rotor with built-in permanent magnets, the rotorcomprising: a) a cylindrically shaped rotor core having: i) a centralaxial hole; and ii) a plurality of openings surrounding the centralaxial hole, each opening has at least four surfaces including a top flatsurface and a bottom flat surface, the top flat surface is adjacent tothe contour of rotor core and extends along the circumference of thecontour to form two side surfaces respectively on two ends of theopening, and a distance is between the two side surfaces and the contourof rotor core; b) a plurality of permanent magnets, each of theplurality of permanent magnets having a cross-section that matches eachof the plurality of openings, each magnet being inserted into one of theplurality of openings; and wherein the two side surfaces in each of theplurality of openings are each parallel with an outer contour of thecylindrically shaped rotor core, the distance is ΔR and ΔR=(R0−Rm)≦0.7mm, wherein R0 is the outer radius of the motor rotor and Rm is thedistance from the center of the motor rotor to the side surface, eachopening further includes two parallel channel side surfaces, and thepermanent magnet for such kind of opening is in corresponding shape,wherein the angle formed by the two adjacent parallel channel sidesurfaces is ΔΘ, and ΔΘ≦[(0.7/Rm)*(360/π)](deg), and Θ₂ is the angledefined by p and ΔΘ, p is the number of the permanent magnets, and whenp≧4,Θ₂=[(360/p)−ΔΘ]](deg), and Θ₁ is the half angle formed by the linesegment between two ends of the top flat surface and the center of themotor rotor, and the length of the top flat surface is 2[(Rm*sinΘ1)],and the length of the bottom flat surface is 2[(Rm*sinΘ2)].
 2. The motorhaving the rotor with built-in permanent magnets according to claim 1,wherein the permanent magnets are positioned with interlaced magneticpoles.
 3. The motor having the rotor with built-in permanent magnetsaccording to claim 1, further comprising a stator having a plurality ofteeth forming an cylindrical interior into which the rotor is inserted,the plurality of teeth being separated by a plurality of slots.
 4. Themotor having the rotor with built-in permanent magnets according toclaim 1, wherein the cylindrically shaped rotor core is made of magneticpermeable material.
 5. The motor having the rotor with built-inpermanent magnets according to claim 1, wherein the cylindrically shapedrotor core includes a plurality of stacked silicon steel pieces to formthe cylindrically shaped rotor core.
 6. A motor having a rotor withbuilt-in permanent magnets, the rotor comprising: a) a cylindricallyshaped rotor core having: i) a central axial hole; and ii) a pluralityof openings surrounding the central axial hole, each opening has atleast six surfaces including a top flat surface and a bottom flatsurface, the top flat surface is adjacent to the contour of rotor coreand extends along the circumference of the contour to form two sidesurfaces respectively on two ends of the opening, and a distance isbetween the two side surfaces and the contour of rotor core, and achannel having a predetermined width is located between two parallelchannel side surfaces; b) a plurality of permanent magnets, each of theplurality of permanent magnets having a cross-section that matches eachof the plurality of openings, each magnet being inserted into one of theplurality of openings; and wherein the two side surfaces in each of theplurality of openings are each parallel with an outer contour of thecylindrically shaped rotor core, the distance is ΔR and ΔR=(R0−Rm)≦0.7mm, wherein R0 is the outer radius of the motor rotor and Rm is thedistance from the center of the motor rotor to the side surface, theangle formed by the two adjacent parallel channel side surfaces is ΔΘ,and ΔΘ≦[(0.7/Rm)*(360/π)](deg), and Θ₂ is the angle defined by p and ΔΘ,p is the number of the permanent magnets, and whenp≧4,Θ=[(360/p)−ΔΘ]](deg), and Θ₁ is the half angle formed by the linesegment between two ends of the top flat surface and the center of themotor rotor, and t is the total thickness of the permanent magnet and isdividable into thickness t1 and thickness t2, wherein t=t1=t2, andt1=Rm(cosΘ₁−cosΘ₂), and the length of the top flat surface is2[(Rm*sinΘ₁)], and the length of the bottom flat surface is2[(Rm*sinΘ₂)−(t2*tanΘ₂)].
 7. A motor having a rotor with built-inpermanent magnets, the rotor comprising: a) a cylindrically shaped rotorcore having: i) a central axial hole; and ii) a plurality of openingssurrounding the central axial hole, each opening has at least foursurfaces including a top flat surface and a bottom flat surface, the topflat surface is adjacent to the contour of rotor core and extends alongthe circumference of the contour to form two side surfaces respectivelyon two ends of the opening, and a distance is between the two sidesurfaces and the contour of rotor core; and a plurality of permanentmagnets, each of the plurality of permanent magnets having across-section that matches each of the plurality of openings, eachmagnet being inserted into one of the plurality of openings; wherein thedistance is ΔR and ΔR=(R0−Rm)≦0.7 mm, wherein R0 is the outer radius ofthe motor rotor and Rm is the distance from the center of the motorrotor to the side surface, wherein each opening further includes twoparallel channel side surfaces, and the permanent magnet for eachopening has a corresponding shape, wherein the angle formed by the twoadjacent parallel channel side surfaces is ΔΘ, andΔΘ≦[(0.7/Rm)*(360/π)](deg), and Θ₂ is the angle defined by p and ΔΘ, pis the number of the permanent magnets, and when p≧4,Θ₂=(360/p)−ΔΘ]](deg), and Θ₁ is the half angle formed by the linesegment between two ends of the top flat surface and the center of themotor rotor, and t is the total thickness of the permanent magnet and isdividable into thickness t1 and thickness t2, wherein t=t1+t2, andt1=Rm(cosΘ₁−cosΘ₂), and the length of the top flat surface is2[(Rm*sinΘ₁)], and the length of the bottom flat surface is2[(Rm*sinΘ₂)−(t2*tanΘ₂)].
 8. The motor having the rotor with built-inpermanent magnets according to claim 7, wherein the two side surfaces ineach of the plurality of openings are straight.
 9. The motor having therotor with built-in permanent magnets according to claim 7, wherein thetwo side surfaces in each of the plurality of openings each have acurved shape.
 10. The motor having the rotor with built-in permanentmagnets according to claim 7, wherein the permanent magnets arepositioned with interlaced magnetic poles.
 11. The motor having therotor with built-in permanent magnets according to claim 7, furthercomprising a stator having a plurality of teeth forming an cylindricalinterior into which the rotor is inserted, the plurality of teeth beingseparated by a plurality of slots.
 12. The motor having the rotor withbuilt-in permanent magnets according to claim 7, wherein thecylindrically shaped rotor core is made of magnetic permeable material.13. The motor having the rotor with built-in permanent magnets accordingto claim 7, wherein the cylindrically shaped rotor core includes aplurality of stacked silicon steel pieces to form the cylindricallyshaped rotor core.